Motor-driven chain saws essentially include three parts: a housing, a drive unit, and a forwardly directed guide bar for accommodating the moving saw chain thereon. The guide bar is secured to the drive unit while the drive unit itself is mounted on an extension arm of the housing with which it is connected via vibration dampers. The housing has a rear handle, extending in the longitudinal direction of the guide bar, and a front handle extending crosswise to the rear handle and secured near the underside of the housing. For reasons of stability, one end of the front handle is secured near the front end of the chain saw on the extension arm, while the other end is secured farther back on the housing on the saw chain side thereof. This arrangement assures that all the handle parts are secured to the housing and is intended to prevent transmission of the inherent vibrations of the drive unit to the handles.
With this arrangement of the housing and drive unit, the extension arm on which the drive unit and one end of the front handle are secured has to take up strong bending and torsional forces during operation, because the transmission of force between the guide bar or drive unit and the handles is effected via the housing, and in particular via the extension arm. For this reason, in known motor-driven chain saws the extension arm is configured as a double-T-shaped profile section. With lightweight metal housings, this embodiment has proved to be strong enough; this is not the case, however, with housings made of plastic, such as polyamide, where under extreme loads permanent deformation of the extension arm occurs.
Since the housings are manufactured from cast parts, it is impossible, for manufacturing reasons, to provide a closed profile section, for instance a box section, although this would be desirable for reasons of strength.